Electric vehicles may comprise one or more electric motors that provide motive power to the vehicle in place of a conventional engine, such as a gasoline or diesel engine. One difference between electric vehicles and conventionally powered vehicles is that the electric motor of the electric vehicle does not “idle” when the vehicle is at rest. Instead, the electric motor is either on, such as when the motor is providing motive power to the vehicle, or off, such as when the vehicle is at rest. This operational characteristic of the electric motor can result in uncontrolled rollback (or roll forward on a downhill). For example, rollback may occur when an electric vehicle starts up an incline from a stopped position on the incline. After the driver releases the brake pedal (but before the driver depresses the accelerator pedal) the vehicle may begin to rollback, down the incline. Uncontrolled rollback may cause driver panic and hazardous driving conditions for the driver of the electric vehicle as well as other drivers.
Some systems for mitigating and/or preventing uncontrolled rollback may utilize regenerative braking to prevent the vehicle from rolling opposite the intended direction of travel. Regenerative braking uses the electric motor of the vehicle to produce electric power from the kinetic energy of the vehicle, thereby braking the vehicle. However, at slow speeds or when the vehicle is starting from rest, the vehicle may have very little kinetic energy and the amount of braking that can be generated by regenerative braking may be insufficient to prevent uncontrolled rollback.
Other techniques to control or prevent vehicle rollback include detecting when rollback occurs and driving the motor of the electric vehicle with sufficient power to prevent the rollback. However, in determining the power to apply to the electric motor to prevent rollback, such techniques do not take into account the rollback acceleration of the vehicle or, more particularly, the differences in vehicle rollback acceleration that may be caused by inclines having different grades.
Accordingly, a need exists for a method and system that can dynamically control the rollback acceleration of an electric vehicle to maintain a desired vehicle speed versus rollback distance regardless of incline, slope and the like.